Braking device for a linear drive

ABSTRACT

A brake device for a linear guide comprising a carrier body ( 1 ) which is movable on a guide rail ( 2 ) and incorporates brake shoes ( 10 ) which act on the guide rail ( 2 ), and a brake piston ( 8 ) which is arranged for displacement by a pressure medium in a brake cylinder ( 9 ) of the carrier body ( 1 ), the brake device further comprising an energy reservoir in form of a compression spring ( 11 ) which acts on the pressure medium that is limited by the brake piston ( 8 ), a piston/cylinder assembly is arranged between the compression spring ( 11 ) and the brake piston ( 8 ), which assembly comprises a unitary control element comprising a displaceable, larger diameter control piston ( 5 ) arranged in a control pressure chamber ( 4 ) to act on the compression spring ( 11 ) and a displaceable, smaller diameter high pressure piston ( 6 ) arranged in a high pressure chamber ( 3 ) to act on the brake piston ( 8 ), a pressure connection ( 13 ) for supply of pressure medium into the control pressure chamber ( 4 ) being disposed on the carrier body ( 1 ).

FIELD OF THE INVENTION

The invention concerns a brake device for a linear guide comprising acarrier body which is movable on a guide rail and incorporates brakeshoes which act on the guide rail, and a brake piston which is arrangedfor displacement by a pressure medium in a brake cylinder of the carrierbody, the brake device further comprising an energy reservoir in form ofa compression spring which acts on the pressure medium that is limitedby the brake piston.

BACKGROUND OF THE INVENTION

Linear guides are used, among other things, in machine tools with highspeed drives, linear platens and laser machining tools. In a brakedevice for a linear guide known from DE-GM 295 05 080, the braking orlocking force is provided by the pressure medium, for example, ahydraulic pressure medium such as oil. However, from the standpoint ofsafety, this linear guide is inadequate because if there is anunintentional drop of pressure in the pressure medium, the carrier bodycan no longer be braked or locked on the guide rail.

SUMMARY OF THE INVENTION

The object of the invention is to create a linear guide whose carrierbody can be braked and locked mechanically in a reliable manner on theguide rail in emergencies such as pressure medium failure.

The invention achieves this object by the fact that a piston/cylinderassembly is arranged between the compression spring and the brakepiston, said assembly comprising a unitary control element comprising adisplaceable, larger diameter control piston arranged in a controlpressure chamber to act on the compression spring and a displaceable,smaller diameter high pressure piston arranged in a high pressurechamber to act on the brake piston, a pressure connection for supply ofpressure medium into the control pressure chamber being disposed on thecarrier body. This results in the formation of a hydro-mechanicalemergency braking system whose braking energy is provided by the energyreservoir situated in the brake device.

The compression spring which acts as the energy reservoir may be a coilcompression spring, a disc spring or spring washers. However, a gaspressure reservoir may also be used for this purpose.

The control piston, the high pressure piston and the compression springcan have a common longitudinal axis extending in the guide direction ofthe carrier body. By this, a large potential stroke of the high pressurepiston which is desirable for safety reasons is obtained.

A compensating reservoir for the pressure medium may be arranged in oron the carrier body and connected by a pressure medium duct to the highpressure chamber and the brake cylinder. Such a compensating reservoirmakes it possible to compensate for wear of the brake shoes and leakagelosses by a refilling of the pressure medium. It is advantageous in thiscase to arrange a one-way valve between the compensating reservoir andthe pressure medium duct.

Advantageously, the compensating reservoir may have a cylindricconfiguration and comprise a displaceable compensating piston for thevariable pressure medium volume of the reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

One example of embodiment of the invention is represented in thedrawings and will be described more closely below with reference to theappended drawings.

FIG. 1 is a side view of a guide rail and a carrier body displaceablethereon, shown in a longitudinal section along line I—I of FIG. 3,hatching being omitted in this and in the following figures;

FIG. 2 is a cross-section through the carrier body supported on theguide rail, along line II—II of FIG. 1;

FIG. 3 is a longitudinal section through the carrier body along lineIII—III of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

The brake device of the invention is conceived as an additionalcomponent for guide carriages of linear rolling bearing guides. A highpressure chamber 3 in the form of a bore and a control pressure chamber4 in the form of a bore coaxial to and with a larger diameter than thehigh pressure chamber 3 are arranged in the longitudinal direction of aguide rail 2 in a carrier body 2 of a linear guide, the carrier body 1being arranged for sliding on the guide rail 2. A control elementcomprising a control piston 5 disposed in the control pressure chamber 4and a high pressure piston 6 disposed in the high pressure chamber 3 issituated in these two bores. The control piston 5 and the high pressurepiston 6 are made as a unitary component. The high pressure piston 6which has the smaller diameter is arranged with a part of its length foraxial displacement in the high pressure chamber 3, while the controlpiston 5 having the larger diameter is arranged, likewise for axialdisplacement, in the control pressure chamber 4.

The high pressure chamber 3 is connected by pressure medium ducts 7 inthe form of narrow, connecting bores to two brake cylinders 9 arrangedin the carrier body 1 and comprising brake pistons 8. One brake piston 8is arranged in each brake cylinder 9 for displacement towards the guiderail 2 in a direction perpendicular to the longitudinal axis of theguide rail 2. Brake shoes 10 are disposed between the brake pistons 8and the guide rail 2. All the pressure chambers, i.e. the controlpressure chamber 4, the high pressure chamber 3, the pressure mediumducts 7 and the brake cylinders 9, are filled with a pressure medium,for example, a hydraulic oil.

The braking energy is not provided from an external source but is madeavailable within the device. This is achieved with an energy reservoirin the form of a compression spring 11 made as a coil spring throughwhich the control piston 5 is supported on an attachment housing 12 thatis screwed onto the carrier body 1.

The control pressure chamber 4 is pressurized by a pressure mediumhaving a pressure of approximately 50 bars supplied through a pressuremedium connection 13. As a result of this, the control piston 5 ispressed against the prestressed compression spring 11 and the highpressure piston 6 is relieved completely of pressure. Thus, the highpressure chamber 3 and the pressure medium ducts 7 connected theretowhich lead to the brake cylinders 9 containing the brake pistons 8, arefree of pressure. In this state, the carrier body 1 is freely movable onthe guide rail 2.

If, on occurrence of an emergency, the control pressure is abruptlyreduced to the ambient pressure of 1 bar, the entire pre-stress force ofthe compression spring 11 is transmitted through the control piston 5 tothe high pressure piston 6. This piston is displaced by the pre-stressforce of the compression spring 11 further into the high pressurechamber 3 where, due to its smaller piston area, the high pressurepiston 6 produces a pressure of several hundred bars in the pressuremedium. This pressure acts through the pressure medium ducts 7 on thebrake pistons 8 arranged in the brake cylinders 9, so that the brakepistons 8 press the brake shoes 10 against the guide rail 2.

To enhance the operating safety and compensate for the wear of the brakeshoes, the device comprises a pressure medium or oil reservoir in theform of an integrated compensating reservoir 14 which is sealed from theenvironment by a readily displaceable compensating piston 15. Thecompensating reservoir 14 is connected through a one-way valve 16 to thehigh pressure chamber 3. If in the course of time, due to wear of thebrake shoes or slight leakage losses at the piston seal of the highpressure piston 6, the high pressure piston 6 were to migrate furtherinto the bore forming the high pressure chamber 3, the force of thecompression spring 11 and, as a result, the braking force would decreaseif no compensating reservoir were provided. However, if the controlpressure chamber 4 of the brake device provided with the compensatingreservoir 14 is pressurized by a pressure medium, for example when theassociated machine is switched on, the control piston 5 compresses thecompression spring 11. This causes the high pressure piston 6 to bedisplaced out of the high pressure chamber 3 so that pressure is removedfrom the brake pistons 8. When a defined partial vacuum is formed in thehigh pressure chamber 3, the one-way valve 16 opens and replenishes thepressure medium as required.

The advantage of having the compensating reservoir 14 is that brakingcan be performed with the full braking force even when there is wear ofthe brake shoes 10. The brake device of the invention which also acts asan emergency brake thus functions maintenance-free and an expensivereplacement of the brake shoes is no longer required.

REFERENCE NUMBERS

1 Carrier body

2 Guide rail

3 High pressure chamber

4 Control pressure chamber

5 Control piston

6 High pressure piston

7 Pressure medium duct

8 Brake piston

9 Brake cylinder

10 Brake shoe

11 Compression spring

12 Attachment housing

13 Pressure medium connection

14 Compensating reservoir

15 Compensating piston

16 One-way valve

What is claimed is:
 1. A brake device for a linear guide comprising acarrier body which is movable on a guide rail and incorporates brakeshoes which act on the guide rail, and a brake piston which is arrangedfor displacement by a pressure medium in a brake cylinder of the carrierbody, the brake device further comprising an energy reservoir in form ofa compression spring which acts on the pressure medium that is limitedby the brake piston, characterized in that a piston/cylinder assembly isarranged between the compression spring and the brake piston, whichassembly comprises a unitary control element comprising a displaceable,larger diameter control piston arranged in a control pressure chamber toact on the compression spring and a displaceable, smaller diameter highpressure piston arranged in a high pressure chamber to act on the brakepiston, a pressure connection for supply of pressure medium into thecontrol pressure chamber being disposed on the carrier body, acompensating reservoir for the pressure medium is arranged in or on thecarrier body and connected by a pressure medium duct to the highpressure chamber and the brake cylinder and a one-way valve is arrangedin the carrier body between the compensating reservoir and the pressuremedium duct.
 2. A device according to claim 1, wherein two brakecylinders are arranged in the carrier body, and each brake cylindercomprises a brake piston to act on the brake shoes and the guide rail.3. A device according to claim 1, the compression spring acting as anenergy reservoir is formed by a coil compression spring, a disc springor spring washers.
 4. A device according to claim 1, characterized inthat the compression spring acting as an energy reservoir is formed by agas pressure reservoir.
 5. A device according to claim 1, wherein thecontrol piston, the high pressure piston and the compression spring havea common longitudinal axis extending in guide direction of the carrierbody.
 6. A device according to claim 1, characterized in that thecompensating reservoir has a cylindric configuration and comprises adisplaceable compensating piston for a variable pressure medium volumeof the compensating reservoir.